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RegulatoryStatus:
Oryzalin is a slightly to practically nontoxic compound in EPA
toxicity class IV. Products containing oryzalin must bear the
Signal Word CAUTION. It is a General Use Pesticide (GUP).

Chemical Class: Not
Available

Introduction:
Oryzalin is a selective pre-emergence surface-applied herbicide
used for control of annual grasses and broadleaf weeds in fruit
trees, nut trees, vineyards, established bermuda grass turf, and
established ornamentals. It inhibits the growth of germinating
weed seeds by blocking cell division in the meristems. It is
available in aqueous suspension, dry flowable, and wettable
powder formulations.

Formulation: It is
available in aqueous suspension, dry flowable, and wettable
powder formulations.

Toxicological Effects:

Acute toxicity: Oryzalin is practically
nontoxic by ingestion, with reported oral LD50 values of
greater than 5000 mg/kg in rats and mice [1,58], and
greater than 1000 mg/kg in cats, dogs, and chickens
[1,106]. The dermal LD50 for technical oryzalin in
rabbits is greater than 2000 mg/kg, indicating slight to
practically no toxicity by this route [58]. It is
reported to cause slight skin and eye irritation in the
rabbit, and no skin sensitization in the guinea pig [58].
It is also slightly toxic when inhaled, with a 4-hour
inhalation LC50 of greater than 3 mg/L in rats [58]. The
formulated products (e.g., Surflan A.S.) may show
moderate toxicity by either the oral or inhalation
routes, and may show skin and eye irritation and skin
sensitization properties [58]. In dogs and cats, large
oral doses cause nausea and vomiting [8].

Chronic toxicity: Rats fed a dietary
level of about 2.5 mg/kg/day for 2 years exhibited blood
changes, increased liver and kidney weights, inhibition
of growth, and decreased survival [8]. Repeated ingestion
of large doses led to adverse changes in blood cell
formation in dogs [8]. Mice given dietary doses of about
200 mg/kg/day for 1 year exhibited decreased uterine and
ovarian weights. Those exposed to doses of 75 mg/kg/day
showed no observable effects [107].

Reproductive effects: There were no
adverse effects on reproduction in a three-generation
study of rats fed dietary concentrations of 12.5, 37.5,
or 112.5 mg/kg/day, the highest dose tested. Fetotoxic
effects appeared at 12.5 mg/kg/day [58,107]. It does not
appear that oryzalin causes reproductive effects.

Teratogenic effects: There were no birth
defects in the offspring of pregnant rats fed dietary
concentrations as high as 112 mg/kg/day for three
generations, nor in the offspring of pregnant rabbits
given doses of 125 mg/kg/day, the highest dose tested
[8,107]. It appears that oryzalin is unlikely to cause
teratogenic effects.

Mutagenic effects: Oryzalin was not
mutagenic in several tests, including tests on live rats
and mice and on bacterial cell cultures [107]. It does
not appear that oryzalin is mutagenic.

Carcinogenic effects: When oryzalin was
fed to rats in doses as high as 135 mg/kg/day for 2
years, there was an increase in the incidence of thyroid,
mammary, and skin tumors [107]. Thyroid tumors and benign
skin and mammary tumors occurred in rats fed a dietary
level of 45 mg/kg/day for 2 years [107]. However, there
were no tumors in mice fed doses as high as 548 mg/kg/day
for 2 years [107]. Because of these conflicting results,
it is not possible to assess the carcinogenicity of
oryzalin.

Organ toxicity: Oryzalin has shown
systemic effects on the thyroid, liver, and kidneys, as
well as blood chemistry, in animal tests.

Fate in humans and animals: Oryzalin is
moderately well-absorbed from the gastrointestinal tract,
and rapidly metabolized and eliminated following
absorption. When oryzalin was administered to male rats,
40% of the dose was excreted in the urine and 40% in the
feces within 3 days. Similar results were obtained in
tests with rabbits, a steer, and with Rhesus monkeys
[106].

Ecological Effects:

Effects on birds: Oryzalin is slightly
toxic to practically non-toxic to birds; the reported
oral LD50 values in bobwhite quail and mallard ducks are
greater than 500 mg/kg, and in chickens is 1000 mg/kg
[1,58]. The 5-day dietary LC50 values in quail and
mallard ducks are greater than 5000 ppm [8].

Effects on other organisms: The reported
oral LD50 for the compound in bees is 11 ug/bee,
indicating it is nontoxic to bees [1,58].

Environmental Fate:

Breakdown in soil and groundwater:
Oryzalin is of low to moderate persistence in the field,
with reported field half-lives ranging from 20 to 128
days [58,11]. A representative value for soil half-life
is estimated to be 20 days [11,58]. Microbial degradation
is mainly responsible for the breakdown of oryzalin in
soils, but it may undergo photodecomposition near the
soil surface [58]. Volatilization is not appreciable
[58]. Oryzalin is slightly soluble in water and it does
not have a strong tendency to adsorb to soil particles
[58,11]. It is bound to a greater extent with increasing
soil organic matter and clay content. In soils with low
proportions of these, high water tables and increased
rainfall, oryzlin may be mobile, and thus present a risk
of contamination to groundwater.

Breakdown in water: No breakdown of
oryzalin by hydrolysis was observed at pH 5, 7, and 9
[8]. Based on its behavior in soil, breakdown by
microbial processes is probably slow in the aquatic
environment due to low levels of oxygen and low microbial
activity. Photodegradation may be significant in the
upper portions of the water column.

Breakdown in vegetation: Oryzalin is
readily absorbed via the roots, and plant metabolism of
oryzalin is minimal [58].

Solubility in Other Solvents: v.s. in
organic solvents such as acetone, methanol, and
acetonitrile; s.s. in benzene and xylene; i.s. in hexane
[1]

Melting Point: 141-142 C [1]

Vapor Pressure: <0.013 mPa @ 30 C [1]

Partition Coefficient: 3.7340 @ pH 7 [1]

Adsorption Coefficient: 600 [11]

Exposure Guidelines:

ADI: Not Available

MCL: Not Available

RfD: 0.05 mg/kg/day [13]

PEL: Not Available

HA: Not Available

TLV: Not Available

Basic Manufacturer:

DowElanco
9330 Zionsville Road
Indianapolis, IN 46268-1054

Phone: 317-337-7352

Emergency: 800-258-3033

References:

References for the information in this PIP can be found in
Reference List Number 10

DISCLAIMER: The
information in this profile does not in any way replace or
supersede the information on the pesticide product labeling or
other regulatory requirements. Please refer to the pesticide
product labeling.